The present invention generally relates to liners for cargo containers, and more specifically, to liners for containers used to carry bulk cargos.
Standardized containers or boxes have come into very extensive use for the shipment of freight by land and sea, and the many advantages of such containers have made it extremely desirable to adapt them for use with as many types of cargo as possible. Accordingly, there have been attempts, with varying degrees of success, to use conventional containers to carry bulk cargo such as dry bulk chemicals, powdered and pelletized resins, flour, coffee and grains.
When cargo containers are used to carry such bulk cargo, it is important that the container itself either be kept clean or be cleaned after each load of cargo is emptied from the container, so that the container can be subsequently used with another load of cargo. Moreover, it is important to protect the bulk cargo from contamination and from undesirable exposure to the natural elements.
For these reasons, large plastic removable liners are often used to line the interior walls or surfaces of the cargo containers that are used to carry bulk cargo. The liner protects the cargo during shipment, for example, from rain and debris; and after the cargo is delivered, the liner can be removed so that the container is again usable, without significant cleaning, to carry other cargo.
Various difficulties have been encountered, however, in using plastic liners in the above-described manner; and in particular, it has been found that the liners often tear or rupture under certain conditions. For example, a cargo container carrying bulk cargo is often emptied by opening the rear doors of the container, and raising the front end of the container to tilt the container so that the cargo slides out the back of the container. Prior art container liners often tear or rupture as the cargo slides rearward through the container and over the liner. Numerous attempts have been made to solve this problem by using braced cardboard or wood bulkheads to help support the liner inside the container, or by hanging the liner from the container roof or walls by means of a multitude of hooks connected to the top perimeter of the liner. These prior art attempts have not been completely successful, however.
It is believed that at least many tears that develop in a liner for a cargo container are caused by wrinkles in the bottom of the liner. Such wrinkles create pockets that trap product inside the liner; and when the container is tilted to empty the product, the weight of the trapped product creates stresses on the bottom of the liner, which may cause the liner to tear.
The number of wrinkles in the bottom of a liner can be substantially reduced or completely eliminated by holding the liner tightly stretched across the interior of the cargo container. If this is done, however, tears or rips may develop in the areas of the liner that are used to secure the liner in place inside the container. To elaborate, a bottom panel of a liner is often simply nailed or stapled to a container floor at a multitude of locations spaced along or adjacent the perimeter of that panel. At the same time, a multitude of ropes may be connected to upper portions of the liner at various locations spaced along or adjacent the top perimeter of the liner, and these ropes may also be connected to hooks on the container walls or ceiling to hold the upper portion of the liner in place. In use, various stresses and forces produced by cargo in the liner, especially if the liner is tightly stretched across the cargo container, may cause the liner to tear partially away from a nail, staple or rope used to connect the liner to the cargo container.